Scientists pinpoint the Great Barrier Reef's life support system

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Scientists have identified the most important reefs that need protecting in the Great Barrier Reef so they can be used to repopulate other reefs.

Australia's Great Barrier Reef is a huge system comprising over 3,800 individual reefs, which makes it the Earth's largest. Located off the northeastern coast of Queensland, it's home to thousands of species. In recent years, however, the Great Barrier Reef has come under threat. Rising sea temperatures have led to a number of problems, including coral bleaching.

Although corals may look like plants, they are in fact animals. Most corals have a symbiotic relationship with algae that live alongside them, and these are often what give the corals their bright colours. The algae photosynthesise, producing energy for themselves and the coral, and the corals keep their side of the bargain by providing a home and nutrients for the algae. But when corals are stressed by high temperatures, they eject their algal bedfellows. This causes them to lose their colour and revert to white, hence the term "coral bleaching".

Loss of their algae partners causes the corals starve and die, setting off a marine domino effect that ripplies through many of the other species that live on the reef, including the fish, crustaceans and plants that live among the corals. Rising sea temperatures have also led to population explosions of crown-of-thorns starfish, which invade reefs and feed on the corals with devastating effects. With these problems on the rise, there is growing concern that the Great Barrier Reef may be completely gone by 2050. With limited funding, scientists want to identify the key parts that need protecting, in order to give the Great Barrier Reef a chance to recover.

This is the thrust of a new study, published this week in PLOS Biology, showing that some parts of the Barrier Reef are more important than others in terms of this recovery.

“We set ourselves three criteria that would be ideally met if there some reefs that were really important in kick-starting recovery of coral,” says University of Queensland study author Peter Mumby. “The first was that the coral reef must be very strongly connected to other reefs downstream. The second was that the reef is more likely to remain standing after bleaching events. The third was that it isn’t a source of pests that eat coral, like the crown-of-thorns starfish.”

For the first criterion, the team used computer simulations to work out whether or not coral larvae from the reef would be able to get to other reefs to repopulate them; second, they used sea temperature records to find reefs that haven’t experienced high temperatures in the past; and third, they used logs of previous crown-of-thorns starfish outbreaks to work out which reefs were the least likely to be sources of these pests.

“We found 112 reefs that met these criteria. That only represents 3% of the Great Barrier Reef, but in a single reproduction event, the larvae released from them can reach almost half of the reefs of the Great Barrier Reef,” says Mumby.

As these reefs have the potential to repopulate so many others, the team believe that by focusing conservation efforts on these key reefs, we could help the Great Barrier Reef recover.

“It might be that some of these reefs warrant additional surveillance and protection. For example, even though they’re less likely to experience crown-of-thorns outbreaks, if they did contract an outbreak you’d want to ensure that boats are sent there to eradicate the starfish.”